Daylighting utilization and uniformity comparison for a concentrator-photovoltaic window in energy saving application on the building

This paper aims to present a novel concentrator-photovoltaic window (CPVW) for the building application, which is able to provide a uniform daylighting environment. In order to study the daylighting performance of the CPVW, the ray-tracing simulation model for the complex window systems are built and validated by the outdoor experimental results. The daylighting uniformity of the proposed window system is analyzed and compared with the state-of-the-art semi-transparent photovoltaic window system (STPVW). The coefficient of variation (CV) is developed to evaluate the daylighting uniformity of photovoltaic windows. It was found that with the use of the CPVW, the daylighting uniformity can be significantly enhanced, while enlarging the active daylighting area at the same time: the CV values are decreased from 0.647, 0.642, 0.606, 0.595, 0.639, 0.624, 0.764 (for the STPVW) to 0.011, 0.044, 0.054, 0.054, 0.113, 0.171, 0.220 (for the CPVW) at various incidence angles. Due to the sun rays reallocation of the concentrator, the active daylighting area can also be enlarged: the ratio of the active illumination area offered by the CPVW to that by the STPVW can be up to 6.69 ×. Thus, with the use of the concentrator-photovoltaic window system on the building, not only can the solar energy utilization be greatly enhanced and does suit the building energy demands well, but also it improves the daylighting uniformity and active natural daylighting area significantly.